Multi-phase voltage regulators are commonly used over single-phase regulators because they produce higher current output, faster transient responses, and more efficient applications in microprocessor power supplies. Due to discrete components and power device mismatches, the load current is not always equally shared among all the phases of multi-phase regulators causing inadequate operation and excessive heat in the power devices of one or more phases of a multi-phase power supply. To overcome this problem, active current sharing may be utilized to force current equalization among all phases. This requires a current sensing circuit. Since sense resistors are both inefficient and expensive, other resistive elements such as RDSon of the power MOSFETs, DCR of the inductor, and board traces are used to measure the source current for each phase of the power supply. These elements have a high degree of variation from one to another over changing environmental conditions and over production lot variations. Historically, using these elements to sense current causes a mismatch in the current between the phases. Currently there are no reasonable solutions to this mismatch.
The droop function is used in a power supply to automatically lower the output voltage based on the output current. This provides more headroom in the case of load transients, and also removes the number of required output capacitors, thus lowering costs while still meeting the required voltage tolerances. The droop is set by the manufacturer of a processor and is based on a function of the regulator output current. Thus, the droop function accuracy is directly related to the current sensing accuracy.
There are many ways to set the droop based on the measured current. For instance, one may limit the DC gain of the error amplifier in the current mode power supply, lower the reference by a ratio related to the overall current, increase the feedback based on the ratio of the overall current, or lower the error based on the ratio of overall current. All these topologies require accurate current sensing and accurate ratio settings at which the load current adjusts the output voltage. Historically, setting the droop accurately has also been a major problem due to inadequacies in current sensing and processor batch variations.
Presently, the droop setting is fixed, thus once the system has been built, the droop rate cannot be changed without overly costly retrofits. Today, variations in processor power requirements vary from processor to processor, even those manufactured by the same manufacturer within the same batch. Because the droop setting is fixed, the power supply is unable to adapt to the processors power needs. Therefore, processors with power specifications beyond what the power supply can produce are wasted. This processor waste is very inefficient and costly.
Another phenomenon affecting current sensing circuit is temperature. Most elements used in current sensing have positive temperature coefficients; the resistance of the circuit increases as the temperature increases. This variation results in erroneous measurements of the current over temperature variations causing further droop inaccuracies.
The present invention provides a cost effective and automated solution to this and other shortcomings of current devices, systems, and methods.